NEW ORLEANS — Humans concerned about the West Nile virus can only slather on DEET-rich repellent, cover their arms and legs when they venture outdoors and obsess about standing water and dead birds on their neighbors' property. But the animals at New Orleans' Audubon Zoo are being vaccinated, even though the zoo's staff isn't sure how much protection the shots will afford.

"We have no knowledge that this will help," general curator Dan Maloney said. "We know that it won't hurt."

Senior veterinarian Roberto Aguilar has given the three-stage vaccine to about 35 animals, including flamingos, cranes and birds of prey, as well as zebras, tapirs and a donkey.

Three Guam rails, tiny birds with brown-and-white-striped feathers, were the latest to receive the shots. Driven into virtual extinction in their native land by the nonnative brown tree snake, the birds are at the New Orleans zoo to breed and build their numbers.

Each rail, which weighs less than 2 pounds, flapped wildly and pecked at Bill McDowell's bare hands as the assistant curator of birds scooped it out of a blue plastic carrier and bore it to a table where Aguilar covered its head with a pillowcase to calm it down.

The pink serum contains killed virus, designed to trigger the production of antibodies. The dose for any animal, from a wee rail to a towering elephant, is the same: one-thousandth of a liter.

The compound zipped onto the market because the path to approval is much quicker for animal medications, Aguilar said.

But Aguilar first drew blood, to be tested to determine if the animal has been exposed to the virus. Maloney said test results have shown the virus in two Audubon Zoo animals: two of six flamingo chicks that died this year.

Tests may show the other four were exposed to the virus, too, he said.

"We know West Nile's all around us," Maloney said. "I wouldn't be surprised if some tests came back positive."

Next on the vaccination list are secretary birds, along with geese and ducks. Because each shot costs nearly $10, Aguilar said he isn't certain whether to give the series to rhinoceroses and elephants because their thick hides probably provide plenty of protection from even the most determined mosquito.

If Aguilar does decide to inject these large animals, the instrument of choice probably will be a dart gun, he said, adding, "Surprise is key."

"There is no secret formula to determine who gets vaccinated and who doesn't," Maloney said, "but if it's too risky to grab an animal up, we'll probably put it at a lower priority."

Although Aguilar acknowledged that there is much to learn about the vaccine and the virus it is supposed to fight, he said there is agreement on this point: There is no need to inoculate house pets, such as cats and dogs, or even spray them with repellent.

Like most humans who are bitten by infected mosquitoes, most animals probably won't display symptoms, he said. The virus can trigger the potentially lethal brain inflammation encephalitis; its symptoms in animals include difficulty in maintaining balance and, in horses, a tendency for the head to droop.